Bulk rubber

Carbon black is the most important additive to rubber comprising between 30% and 70% of the bulk rubber product. Tire goods consume about 65% of the carbon black, mechanical goods another 25%, with only about 10% employed for nonrubber applications. 

We will look at the processing involving bulk rubber. The manufacture of rubber products from this material can be divided into four steps ... 

Fig. 33 Schematic view considering the structure of filler-filler bonds in a bulk rubber matrix. The impact of gap size on the stiffness of filler-filler bonds becomes apparent...

In the case of cellular rubber, the ASTM uses several classifications based on the method of manufacture [11,12]. Cellular rubber is a general term covering all cellular materials that have an elastomer as the polymer phase. Sponge rubber and expanded rubber are cellular rubbers produced by expanding bulk rubber stocks, and are open-cell and closed- cell, respectively. Latex foam rubber, which is also a cellular rubber, is produced by frothing a rubber latex or liquid rubber, gelling the frothed latex, and then vulcanizing it in the expanded state. 

After the microwave techniques, ultrasonic energy was used for the devulcanization of cross-linked rubber. The first work with ultrasonic energy was reported by Pelofsky in 1973, which was patented.In this process solid rubber articles such as tires are immersed into a liquid, which is then kept under a source of ultrasonic energy whereby the bulk rubber effectively disintegrates upon contact and dissolves into liquid. In this process ultrasonic irradiation is in the range of about 20 kHz and at a power intensity of greater than 100 W. 

Proton spin resonance measurements on carbon black filled rubbers confirm the relatively small effect of the black on local segmental mobility. Waldrop and Kraus (107) were unable to find evidence for two spin-lattice relaxation times (one for surface rubber and one for bulk rubber) and found very little effect of carbon blacks on the position of the minimum in the spin-lattice relaxation time (7j) vs. temperature curve. The shape of the curve was also substantially unaffected (107). Extraction of free rubber from an uncross-linked SBR-HAF black mix did not accentuate the effect of the carbon black. More recently Kaufmann, Slichter and Davis (108) reported the observation of two spin-spin relaxation times (T2) in the bound rubber phases of polybutadiene and ethylene-propylene rubber, each reinforced with 50 phr of an SAF black (155 m2/g surface area). The amount of fully immobilized polymer was only 4% of the total, but the remainder of the bound rubber displayed... 

How to solve this problem is difficult to state and many approaches can be taken. Alternative forms of transportation such as pipelines for liquids and sometimes solids, water movement, truck-rail (piggy-back), and truck-water (fishy-back) combinations, are all possibilities. Plant relocations to minimize shipping distances to major customers, or to allow direct across -the-fence movements, should be considered. The use of the newer, or the yet-to-be-developed containers, such things as bulk rubber bags for liquids, bulk handling of dry solids via air slides, etc., lined fiber drums for liquids, should all be carefully studied. The creation of bulk distribution points may in some instances be of value. 

The molecular weight of uncrosslinked rubbers is measured by the same techniques applied to other addition polymers. The concept of a molecular weight for individual chains is not applicable to bulk rubber crosslinked to a degree exceeding the gel point rather, the concept of chain length between tie points is substituted. The use of swelling liquids to elucidate this quantity is described in Chapter 7, Section 8. 

O Malley M, Mathias C, Priddy M, et al. (1988) Occupational vitiligo due to unsuspected presence of phenolic antioxidant byproducts in commercial bulk rubber. J Occup Med 30 512-516... 

Commercialization Update. High quality guayule latex rubber and bulk rubber can both be produced from guayule, but the economics of latex production... 

There are several drawbacks to the use of self-bonding compounds which are worthy of mention. To make a self-bonding compound, one must modify the properties of the bulk rubber compound in order to affect the chemistry of the reactions which are required to take place only at the rubber to metal interface. Processing is adversely affected since the compounds want to bond to the mould and metals alike, and the environmental resistance of the rubber to metal bond is generally poor compared to that which is obtained with the use of a conventional rubber to metal adhesive system. 

In extending the calculations to include all the cartesian components, it is necessary to keep in mind that the volume of a bulk rubber changes very little when the rubber stretched. It is sufficient to set x equal to unity. 

Figure 3 Transmission electron micrographs of (a) a functionalized bulk rubber and (b) a functionalized core/shell modifier, dispersed in nylon 6. (20 wt% loading in both cases.)...

Core/ shell particles can be less efficient than bulk rubbers as toughening agents, because they contain less rubbery material. On the other hand, the hard shell has been well documented to have a less deleterious effect on matrix stiffness than that observed with bulk rubbers. 

The present approach is to treat the behaviour of the particle as solely responsible for the mixing behaviour. Also, the behaviour of the particle is assumed to be characterised by testing the bulk rubber [16]. 

In general, the volume term is expected to be small. In bulk rubbers this is true because the volume change on deformation is small in swollen rubbers x will be large and will probably be small. Nevertheless, experimental observations showing that the volume term does not vanish can be interpreted on the basis of assumptions (46) or (46 ). 

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